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MVN Calibration

Calibration is important to initialize the orientation of the Motion Trackers and to ensure magnetic immunity. A good calibration can therefore greatly improve the Motion Capture data quality. This article explains the best practices when performing a calibration.

See also:
- Calibrating Link Tutorial
- Calibrating Awinda Tutorial

 

1. Calibration 

Below, the recommended Npose + Walk calibration is explained in detail. 

1. To start calibration, select one of the systems to be calibrated

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2. Select Npose + Walk (Recommended) and click Calibrate (see chapter 2. Calibration Routines,  below).   

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3. Assume the Npose 

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4. Press Start

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5. Hold the Npose for 2.5 seconds.
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6. Walk forward for about 5 seconds (you can swing your arms).
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7. Make a smooth u-turn
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8. Walk back to the starting position.
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9. Turn around at the starting position and stand in Npose again. 
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10.  Wait until MVN indicates that it started processing the calibration. You can now relax, but don't make any quick movement (e.g. stomping on the ground or clapping your hands). 
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11. When MVN is finished with processing, it will give the calibration results. You should aim for a "Good" result (see chapter 3. Calibration Results below).

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12. When satisfied with the Calibration result, presume Npose at the location you want to define the x-axis (see chapter 4. Applying Calibration, below)
13.  Click Apply, Subject is standing in N/Tpose
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14. The calibration will be applied. 
15. Walk around the room for about 10 seconds to warm up yourself and the system (see chapter 5. Walk around after calibration, below)
16. You are now ready to start recording. 

  

2. Calibration Routines

Below, different calibration routines are described. For the best results, the Npose + Walk is the recommended calibration routine. The Npose is in general an easier pose, because the arms can be relaxed making it easier to keep still. The walk is recommended to ensure full magnetic immunity.

2.1 Npose + Walk (Recommended)

Npose (2.5 seconds)

- Stand upright on a horizontal surface.
- Feet parallel, one foot width apart.
- Knees above feet.
- Hips above knees.
- Back straight.
- Shoulders above hips; do not lift shoulders up.
- Arm straight alongside body (vertically), thumbs forwards.
- Face forward.
- Do not move during the Npose procedure.

Walk (5 + 8 Seconds)

- Relax and start walking forward like you are walking down the street. You can swing your arms naturally during this walk. Try to avoid quick motion (e.g. stomping on the ground or clapping your hands). 
- after about 5 seconds of walking make a smooth U-turn. You can do this by continuing walking while making the U-turn. Try to avoid quick motion (e.g. a hard stop and turn).
- After the U-turn walk back to the starting position again in a similar fashion as described above. 
- When arriving at the starting position, make a smooth U-turn again so you are facing the same way as you did when you did the first N-pose. 
- When you are at the starting position and orientation, stand in N-pose again and wait until the Calibration Routine is over. When MVN starts Processing the calibration data, the Calibration Routine is over and you can relax. you can now walk around, but make sure you don't make any quick motion (e.g. stomping on the ground or clapping your hands or bumping into obstacles). 

 

2.2  Tpose + Walk

Npose (2.5 seconds)

- Stand upright on a horizontal surface.
- Feet parallel, one foot width apart.
- Knees above feet.
- Hips above knees.
- Back straight.
- Shoulders above hips; do not lift shoulders up.
- Arm straight stretching sideways (horizontally), thumbs forwards.
- Face forward.
- Do not move during the Tpose procedure.

Walk (5 + 8 Seconds)

- Relax and start walking forward like you are walking down the street. You can swing your arms naturally during this walk. Try to avoid quick motion (e.g. stomping on the ground or clapping your hands). 
- after about 5 seconds of walking make a smooth U-turn. You can do this by continuing walking while making the U-turn. Try to avoid quick motion (e.g. a hard stop and turn).
- After the U-turn walk back to the starting position again in a similar fashion as described above. 
- When arriving at the starting position, make a smooth U-turn again so you are facing the same way as you did when you did the first Tpose. 
- When you are at the starting position and orientation, stand in Tpose again and wait until the Calibration Routine is over. When MVN starts Processing the calibration data, the Calibration Routine is over and you can relax. you can now walk around, but make sure you dont' make any quick motion (e.g. stomping on the ground or clapping your hands or bumping into obstacles). 

 

2.3 Npose (Not Recommended)

CAUTION: This calibration is not fully magnetic immune and is therefore not recommended. It is not available by default. To enable this routine, go to Options > Preferences > User Interface > Enable simple calibration routines.

Npose (2.5 seconds)

- Stand upright on a horizontal surface.
- Feet parallel, one foot width apart.
- Knees above feet.
- Hips above knees.
- Back straight.
- Shoulders above hips; do not lift shoulders up.
- Arm straight alongside body (vertically), thumbs forwards.
- Face forward.
- Do not move during the Npose procedure.

 

2.4 Tpose (Not Recommended)

CAUTION: This calibration is not fully magnetic immune and is therefore not recommended. It is not available by default. To enable this routine, go to Options > Preferences > User Interface > Enable simple calibration routines.

Tpose (2.5 seconds)

- Stand upright on a horizontal surface.
- Feet parallel, one foot width apart.
- Knees above feet.
- Hips above knees.
- Back straight.
- Shoulders above hips; do not lift shoulders up.
- Arm straight stretching sideways (horizontally), thumbs forwards.
- Face forward.
- Do not move during the Tpose procedure.

 

3. Calibration results

3.1 Results

After calibration has been processed, MVN will give an indication of the calibration results. Possible outcomes are (ordered from best to worst):

- Good
- Acceptable 
- Poor
- Calibration not performed ye

Generally, a Good or Acceptable quality indication is sufficient. If the result is Acceptable, consider repeating.

NOTE: A Good or Acceptable quality indication does not necessarily mean that the actual calibration is accurate. MVN Analyze/Animate can perform limited checks of the actual pose of the subject during the calibration due to a natural variation in body physique and locations of the motion trackers on the body. Therefore, always pay attention to the pose of the subject since it will influence the quality of the recording.

3.2 Improvements

If the calibration result is not Good, the reason is indicated in the text below. Read the advice provided to improve the result. Some examples are shown below.

Calibration cannot be performed, because the required Body Dimensions are not set!
Before calibration, make sure to set the Body Dimensions of the system you are calibrating. You can change the body dimensions in the Motion Capture Configuration window (see the article on Body Dimensions).

Clipping in data
Some movement during the calibration was sudden (e.g. stomping on the ground or clapping your hands). Make sure to relax and perform a smooth walk and u-turn. 

Please hold SEGMENT still during static pose / Too much movement in SEGMENT during static pose / Static pose part is very short or not existing
The talent was moving too much during the static pose or started walking too early. Make sure that all segments are still during the static pose. If this is difficult, you could press your arms to your sides or stand with your back and heels against a wall for support during the static pose. 

SEGMENT most likely not in desired static pose
The mentioned SEGMENT is not in the correct pose. Double-check the correct pose in chapter 2. Calibration Routines.

Sensor placement SEGMENT estimated poorlyCheck sensor orientation of SEGMENT
The Motion Tracker on the mentioned SEGMENT might not be placed correctly. You can check Motion Tracker placement in these articles:
- Link
- Awinda

Walking detected during static pose part
The talent has started the walking part to early in the calibration routine. Hold still until the static pose timer completely runs out. Then, relax and start the walking phase. 

Walking part is very short or not existing
The walking part was too short. Make sure that you spent enough time on the walking part. If you have a small space, you can try to walk a bit slower. 

Quality of calibration solve is poor / lower than expected
It is possible that one or more trackers are swapped in location. Check the avatar and see if the movement of a Motion Tracker corresponds with the correct Avatar Segment. For example, to check the left hand Motion Tracker, only rotate your left wrist and monitor if the avatar also rotates the left wrist. 

Magnetic field near SEGMENT seems heavily disturbed / Magnetic field is disturbed, check if you are standing near ferromagnetic objects
There is too much magnetic field interference in the environment you are recording. It is recommended to perform a calibration routine with a Walk included to remove these disturbances. If a calibration with walk is not desired or not possible, it is recommended to move to a location with less interference. 

3.3. Results of Recorded file

It is also possible to see the calibration results of recorded files. If a recorded MVN file is opened, the calibration results will be displayed in the Hardware Setup pane (by default on the bottom left in MVN). 

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4. Applying Calibration

When you apply the calibration, that will define that system's origin and heading. The right heel will be defined as the origin (0.0.0 in the X,Y,Z global coordinate system) and the way you are facing will dictate the positive X-axis. The origin with front-facing x-axis is indicated in MVN by a red triangle.

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1. Stand in Npose/Tpose with your right heel on the preferred origin and facing the direction of your preferred X-axis
2. Press Apply,subject is standing in N/Tpose

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To reset the position and/or orientation of the characters in between recordings, select the character in the navigator and perform the required reset:
- Reset position (Tasks > Move Character to Origin, or press Ctrl-0 (Ctrl+[Zero Key]).
- Reset heading (Tasks > Axis Reset, or press Ctrl+Alt+A).
- Reset position + heading (Tasks > Grid Reset , or press Ctrl+Alt+G).
- Reset mocap engine (Tasks > Reinitialize Mocap Engine, or press Ctrl+Alt+F). Please note that this step means all history in the engine is thrown away and the engine will start from scratch.

 

5. Walk around after calibration

To get some initial data in the MVN Engine ("warm-up the filters"), it is required to walk around for about 10 seconds after applying calibration and before you start a recording. Doing so will increase the motion capture quality. There is no specific routine or path the talent has to walk, but for ease of use, you could walk in a circle around the room or walk in a figure 8.

NOTE: It is not required to warm-up the filters before every recording, just after applying a calibration. 

Once you're done with walking around, you are ready to start the Recording. 

 

6. Save/Load Calibration

After a calibration has successfully been applied, it can be saved. 

NOTE: Save/Load Calibration is only available in MVN Animate Pro and Analyze. 
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This is useful if MVN Analyze/Animate closes/must be closed suddenly. When rebooting, data can be reloaded, without having to re-calibrate. To reload a calibration (including body dimensions), click Load.

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After loading the calibration, walk around for a bit (see chapter 5. Walk around after calibration).

NOTE: Loading a calibration is only useful if no Motion Trackers have moved significantly in between the saving and loading of the calibration. If Motion Trackers have moved in between, a new calibration is recommended. 

7. Hands-off calibration

The hands-off calibration is a function that introduces a timed delay to the calibration steps, making sure that you have enough time to get into position when you are operating MVN by yourself. 

The hands-off calibration can be found in the Hardware setup window, under the Calibration Tab (on the left-hand side in MVN by default). 

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1. Enable the Hands-off calibration and set the delay of this hands-off calibration before starting the calibration. Make sure the delay is enough to walk to the starting location of the calibration and to the spot where you want to apply the calibration. 

- The minimum delay is 2 seconds
- The maximum delay is 16 seconds
- The default delay is 6 seconds

2. Click Calibrate
3. Click Start > the timed delay will start.mceclip11.png

4. Walk to the position to start the calibration.
5. When the timer runs out, perform the Calibration Routine.
6. After the calibration routine, MVN will process the calibration and indicate the result.
7. If you are satisfied with the result, press Apply > the timed delay will start.
8. Walk to the position you want to apply the calibration to and stand in Npose.
9. When the timer runs out, the calibration is applied. 

 

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